In an “ad hoc” computer group, each computer directly talks to and shares computing resources and services with other computers in the group. This type of group allows the collective computing power of all members to benefit the entire group. For example, a large computational job calling for significant computational power and resources can be distributed across multiple members of the group, and computation results can be shared directly among the members of the group. Moreover, this type of group allows new members to join the group that never connected to the group before.
For managing and supporting the ad hoc group, each computer takes one of three basic roles, the roles defined by privileges to interact in given ways with other group members. The three basic roles are owner, inviter, and authenticator. The owner establishes the group and has all the privileges defined in the group including the privilege to invite a new member to join the group, the privilege to authenticate a new member and thus to admit the new member to the group, the privilege to change the role of a member, and the privilege to change information about the group. An inviter has the same privileges as the owner except for the privilege to change group information. An authenticator may authenticate a new member into the group, but does not have the privilege to invite the new member to join the group.
Security is one of the major concerns in an ad hoc group. In order to keep the group secure, a new potential member, when trying to join the group, exchanges authentication proofs with an authenticator in the group. This authentication process is repeated by the new group member with every group member with whom the new group member wishes to directly converse. (A first group member may indirectly converse with a second member with whom it has not been authenticated by passing information through a third member with whom the first and second members have been authenticated. This indirect communications method is always available, but does not affect the discussion of the present invention and will not be mentioned again.) Unlike groups with a fixed membership, in an ad hoc group new members may ask to join the group at any time. It is almost impossible for an authenticator in the group to maintain authentication information for all potential members of the group.
Making authentication in an ad hoc group even more of a problem, the new potential member may wish to converse with an authenticator that does not have the privilege necessary to invite the new member to join the group. For example, Alice intends to join an ad hoc group in order to converse with authenticator Bob. Trent is an inviter in the group. Alice gets an invitation to join the group from Trent, but she now wants to be authenticated by Bob in order to converse with him. While Trent trusts Alice (else he would not have invited her to join the group), and while Bob trusts Trent and trusts the invitation Trent gave to Alice, Bob knows nothing about Alice and, hence, does not trust her. Before allowing Alice to join the group, Bob needs to transfer some of his trust for Trent to Alice.
What is needed is a mechanism for an authenticator in a group to securely transfer its trust of an established inviter in the group to a potential group member.